Patent GB-1297350-A (GB)
IPC: C08J3/24
Filed: 1971-05-04
Abstract: 1297350 Moulding plastic substances DOW CORNING CORP 4 May 1971 [1 June 1970] 12983/71 Heading B5A [Also in Divisions B2 and C3] Silicone elastomer is grown on a mould or former by placing the substrate having a curing catalyst for an uncatalysed silicone elastomer composition on the surface thereof in contact with an uncatalysed silicone elastomer composition for a time sufficient to grow silicone elastomer on the surface of the substrate and thereafter removing the substrate from the uncatalysed silicone elastomer composition. Preferably the substrate is first coated with a thin coat of an uncatalysed organosiloxane elastomer composition, e.g. by dipping, and the curing catalyst then applied over the uncatalysed organosiloxane elastomer composition by spraying, dipping or powdering. The uncatalysed organosiloxane elastomer in the subsequently applied coating can be the same as or different from the first coating. In another embodiment, the substrate is first dipped in an organic solvent dispersion on an uncatalysed organosiloxane elastomer composition which comprises an organosiloxane polymer and a filler, then coated by dipping with the uncatalysed organosiloxane elastomer composition in an organic solvent solution of a cross linker for the organosiloxane polymer and a curing catalyst for the organosiloxane polymer and cross linker combination and subsequently placed in an organic solvent dispersion of an uncatalysed organosiloxane elastomer composition for at least one minute. This method applies especially when the crosslinker is trimethoxysilane. The final product may be exposed to an air atmosphere before dipping again in the curing catalyst solution before exposure to curing conditions. The method may be carried out in an organic solvent atmosphere to produce a glossy finish. The steps can be repeated to build up thick coatings. The substrates can be glass, metal, e.g. copper, aluminium, steel, paper, fabric, thermoplastics, rubber, resins, wood and ceramics in the form of, e.g. sheets, rods, coils, printed circuits, cloth, screen, television transformers. The uncatalysed organosiloxane elastomer composition can be vibrated to provide maximum penetration in all the surface irregularities of the substrate. The ground silicon elastomer may be removed from the substrate to provide a silicone elastomer device, e.g. a medical device such as catheter, T-tube, endotracheal tube with cuffs and suprapubic drains. Suitable silicone elastomer compositions comprise hydroxyl end blocked diorgano polysiloxane and alkoxy silicon compounds; alkenyl polydiorgano siloxane, and an organo hydrogen siloxane. In Example 7 the uncatalysed siloxane elastomer composition comprised a dispersion of 100 parts hydroxyl and blocked polydimethyl siloxane having a viscosity of 12,500 cs., 40 parts of a reinforcing silica filler having a trimethyl siloxy surface treatment, 210 parts toluene, 1À4 parts phenyl trimethoxy siloxane and 2À8 parts The catalyst solution comprised 10 parts stannous octoate, 0À4 parts trimethoxysilane, 0À8 parts of (I) prepared by refluxing a mixture of equal molar amounts trimethylsilanol and phenyl trimethoxy silane in the presence of potassium acetate catalyst, 22 parts trimethyl siloxy end blocked polydimethyl siloxane having viscosity 0À65 cs. and 67À8 parts toluene. In Example 8 a catheter was prepared by dipping a catheter form having a release agent on its surface in a dispersion of 100 parts hydroxyl end blocked polydimethyl siloxane, 18 parts reinforcing silica filler having trimethyl siloxy surface treatment, 2À4 parts phenyl trimethoxy silane and 118 parts of toluene, dipping in a catalyst solution of 20 parts stannous octoate and 80 parts trimethyl siloxy end blocked polydimethyl siloxane, immersing the catalyst containing catheter form in the dispersion and allowing silicone rubber to grow for 10 minutes and thereafter air drying for 15 minutes at room temperature. The catheter was dipped in the catalyst solution of the dispersion for 10 minute growth periods for four additional growth periods. The immersion and withdrawal rate was 1À27 centimetres per minute. The catheter was allowed to cure and removed from the form.